1. Field of the Invention
The present invention relates to a leak inspection device in which air leakage from an object to be inspected is detected with a leakage inspection medium (tracer gas) such as helium gas (He gas).
2. Description of the Related Art
Concerning prior art inspection methods to inspect a minute gas leak in an object to be inspected, an inspection method has been provided in which a helium gas leak detector, to detect helium gas which has leaked out from an object to be detected, is used. An example of this inspection method is a vacuum type helium gas leak inspection method in which the gas leak inspection device shown in FIG. 6 is used.
In the vacuum type leak inspection device shown in FIG. 6, an inspection is conducted according to the inspection flow shown in FIG. 8, which will be described as follows. A product 1, which is an object to be inspected, is accommodated in a vacuum chamber 2, and a pipe for charging He gas is connected to the product 1. Next, a vacuum pump 3 is operated so as to discharge air from the vacuum chamber 2. When the degree of vacuum in the vacuum chamber 2 has reached a predetermined value, for example, when the degree of vacuum in the vacuum chamber 2 has reached 10 Pa, the vacuum pump 3 is stopped so as to stop an air discharging operation and the product 1 is filled with He gas supplied from He bomb (gas cylinder) 4. At this time, He gas is supplied until the pressure of He gas in the product 1 is raised to 1 MPa. Next, He gas, which has leaked out from the product 1, is introduced into a leak detector 5 and a volume of the leakage gas is measured by utilizing a mass spectrometry method. According to the result of the measurement, the quality of the product 1 is judged.
However, there are various sizes of products to be inspected. Therefore, as shown in FIG. 7B, it is necessary to determine a size of the vacuum chamber so that a product of the maximum size can be accommodated in it. Accordingly, in the case where a small product is tested as shown in FIG. 7A, the unused space is inevitably large as compared with the size of the product. Accordingly, it is necessary to discharge a large volume of air. As a result, it is necessary to provide a large capacity air discharge pump to discharge air from the vacuum chamber. Further, it takes a long time to discharge the air from the vacuum chamber.
Also, when the volume of the vacuum chamber is large, the concentration of the He gas which has leaked out from the product is low in the vacuum chamber. Accordingly, the measurement sensitivity is deteriorated.